I. Field of the Invention
This invention relates generally to apparatus for detecting flaws in tires and, more specifically, to a high-voltage tire testing system for detecting the presence of nails and/or cuts and holes in tires for wheeled vehicles.
II. Discussion of the Prior Art
In the tire retread industry, visual testing is performed on used tire carcasses to ensure that they are free from cuts, holes and nails. In this regard, it is essential that the testing be accomplished in a minimum of time, yet with reliability so as to ensure that all defective carcasses are culled. The cuts and holes of culled carcasses can then be patched and the nails removed, prior to buffing and retreading.
While visual inspection is reasonably accurate, flaws frequently are missed, due either to human error or to the lack of visible evidence. Missed flaws, during retreading, can create problems in that they allow high pressure air to force its way through the flaws and into the tire structure, causing separation, heat and degradation of the tire, and which in turn can cause a failure of the tire either in the retread shop ("mold blows") or failure of the tire on the road.
At the present time machines do exist for finding holes in tires in retread shops and elsewhere. These machines, however, generally involve tire inflation followed by observation of escaping air either ultrasonically, with bubbles, etc. It is therefore an object of the present invention to permit such testing without inflating the tire and in a fashion that lends itself to the operations of a retread shop. In this regard, the advantages of the present high-voltage method and apparatus to find holes in tires and as hereinafter described in detail are:
1. Detection of extremely small holes down to pinhole size;
2. Detection of holes, cuts or cracks in the inner liner, which penetrate from the inside of the tire into the cord or tread rubber, but do not pass through the tire; such flaws being as important to locate and patch as those that go through.
3. Detection of holes in tires that were retreaded with holes in them and which holes are on the inside and not through the tire.
4. Detection of offset holes where the hole path from the inside to the outside is not-in-line, but rather is connected by a channel through the cord. In such cases, the escaping air is observed in the conventional inflation method on the outside of the tire, while the inside hole location (i.e., the location to be patched) is found by the present invention.
5. Detection of nails, screws, etc. that remain in the tire and which can be removed after test and the hole patched.
6. Detection in certain instances of internal separations in the tire.
7. Simple, fast and easy to use apparatus, that does not require tire inflation, and thereby permits simultaneous visual inspection while performing a high-voltage inspection.
Up to the present, there is no known commercial machine for use in retread shops using high-voltage methods to detect and locate nails, cuts, holes and other flaws in tires. While high-voltage methods for finding holes and flaws in insulating materials are known and have been used in the past, they have never been applied to tires. The application of these methods and new and novel apparatus for finding flaws in tires is therefore the subject of the present invention.